A method of the above kind is known from the marketplace. A corresponding internal combustion engine includes a so-called variable valve control. Variable valve controls of this kind afford the advantage that (especially in internal combustion engines which can be also operated at high rpms) the requirement for reduced exhaust-gas emissions and low consumption can be well satisfied at high rpms (in the maximum power range) as well as in the mid rpms (in the range of the best torque) and, finally, also at low rpms.
Usually, the inlet valves of internal combustion engines are actuated by a camshaft. With these camshafts, the crankshaft of the engine opens and closes the corresponding inlet valve at a specific opening angle or closing angle, respectively. The valve stroke curve is determined by the form of the cam when the inlet valve is actuated by a camshaft. The phase position of the valve stroke curve is usually likewise referred to the cylinder-individual angle of the crankshaft of the engine and is dependent upon the angular position of the camshaft relative to the crankshaft.
From the state of the art, various types of variable valve controls are known. Accordingly, it is possible to rotate the camshaft during the operation of the engine as required about its longitudinal axis relative to the crankshaft. The rotation of the camshaft is possible continuously between two end positions. In this way, the phase position of the valve stroke curve can be changed continuously between two end positions.
It is also possible to displace a camshaft in the longitudinal direction having cams with a profile which changes in the axial direction of the camshaft. In this way, all of the above-mentioned parameters can be changed.
Furthermore, there are camshafts where there is not only one cam profile but there are two cam profiles arranged in pairs for controlling an inlet valve. With a shift of such a camshaft in its longitudinal direction, a selection can be made between the two valve stroke curves which are pregiven by the respective cams.
With such a switchover from one valve stroke curve to another, the problem is presented that, without corresponding countermeasures, various condition variables of the combustion in the combustion chamber and, as a consequence, also the torque of the engine, can suddenly change. If, for example, there is a switchover from a valve stroke curve having a long valve stroke to a valve stroke curve having a short valve stroke, there is suddenly less fresh air getting into the combustion chamber which, in turn, has the consequence of a corresponding jolting of the engine.
So that no sudden jump in torque of the engine occurs, up to now, the following are synchronized with high complexity: the stroke switchover, the drive of the throttle flap of the engine, the output of an ignition angle and the injection of fuel into the combustion chamber.
The control of this synchronization requires a knowledge of the switchover time point as precise as possible which can be clearly delayed with respect to the drive itself in a hydraulic shift system and here especially when the oil is cold. Furthermore, the diagnosis of such a system is also very complex. The diagnosis is necessary because an incorrect shift position (for example, also of only one cylinder) can lead to misfires or unwanted accelerations or decelerations of the engine. This is furthermore possible even at low or mid rpms.